As the demand for better connectivity to the internet grows, there is an ever increasing need for greater bandwidth. Therefore, modern communication systems have been optimized to achieve higher data rates. As the data rates increase, reliable communication becomes difficult due to signal integrity constraints. The channel through which the data is transmitted has limited bandwidth and other physical impairments, such as dispersion.
Electronic receivers with built-in filtering capability attempt to overcome some of these physical limitations, and have superior performance. In testing the performance of such receivers under laboratory conditions, there is a need to generate a wide range of artificially distorted pulses. The collection of these ‘stress-test’ pulses should cover the range of channels the receiver is likely to encounter. A generic two-pulse response can be used to model a wide range of channel responses. This can be done varying the shapes of the two pulses, and their relative amplitudes and spacing. Embodiments of the present invention deal with the artificial generation of stress-test pulses with a two-pulse response.
A conventional method to generate a generic two pulse-response is to use a feed-forward network. The circuit is shown in FIG. 2. A band-limited input source is split into two paths through a matched resistive power splitter/combiner of Δ or Y configuration. The differential delay between the two paths is controlled to generate the proper spacing for the final desired pulse. The resulting pulses are then buffered by high-speed isolation amplifiers, which are matched on both ports. These isolation amplifiers ensure that the path from the input to the output is unidirectional. The amplifiers may have different gains to generate a wide variety of pulse shapes.
The buffered pulses are then merged together via another resistive combiner to drive the output. Any returning pulses which do not go towards the output are terminated at the outputs of the high-speed amplifiers. Without the high-speed amplifiers, signals which couple from one path into the other will re-circulate and corrupt the final output signal. One such path is shown in FIG. 3.
One drawback of using this approach is the need for discrete high-speed amplifiers. For 10 Gigabit Ethernet signals, the bandwidth of these high-speed amplifiers may need to be 5 GHz or higher. Such amplifiers are expensive, and without the active amplifiers, the effect of these re-circulating signals can be mitigated by the insertion of passive attenuators in the two data paths. The result is an uncomfortable tradeoff between mitigation of the runt pulses, and desired signal amplitude.
Accordingly, there remains a need for a system and method that generates generic two pulse responses preferably without the use of expensive, high speed off-chip amplifiers. Embodiments of the present invention disclose a method and apparatus for artificial generation of a generic two pulse response without using such amplifiers.